Underride Accidents: Why They Are So Deadly (and Often Preventable)

Underride happens when a smaller vehicle slides beneath the body of a tractor-trailer — usually under the rear or side. Because the trailer floor strikes the windshield directly, fatality rates are extraordinarily high. The Insurance Institute for Highway Safety estimates more than 400 underride deaths per year in the U.S., a number widely viewed as underreported due to inconsistent police coding.

Rear underride

Federal regulations require rear underride guards (the "Mansfield bar"), but the original standard dates to 1953 and current FMVSS 223/224 standards have not had a substantive upgrade since the late 1990s. Many existing guards fail in real-world crashes because they were tested only at low speeds and direct angles.

Side underride

Most U.S. trailers still have no side underride guards at all, despite IIHS testing showing that effective guards prevent fatal underride at speeds up to 40 mph. Several major carriers have voluntarily started installing them — the absence of one on a defendant's trailer is increasingly being argued as negligence.

Liability theories

Underride cases commonly target: the motor carrier (for inadequate guards or poor maintenance of the existing ones), the trailer manufacturer (product liability), and the maintenance provider (for failing to inspect or repair damaged guards).